A robust phase oscillator design for wearable robotic systems

The design of a phase-based robust oscillator for wearable robots, that could assist humans performing periodic or repetitive tasks, is presented in this paper. The bounds on perturbations, that guaranteed the stability of the output for the phase oscillator controller, were identified and the Lyapunov redesign method was applied to construct a robust controller using a bounding function. The robust controller produced a bounded control signal to modify the amplitude and frequency of the resulting second-order oscillator to modulate the stiffness and damping properties. In this paper, the focus is on the mathematical modeling of the controller, its dynamic stability and robustness for human–robot application. The proposed approach was verified through a simple pendulum experiment. The results provided evidence that a better limit cycle, with a controlled radial spread of the steady state, was obtained with Lyapunov redesigned phase oscillator. Finally, the potential of the proposed approach for hip assistance in a healthy subject wearing HeSa (Hip Exoskeleton for Superior Assistance) during periodic activities are discussed with preliminary results.